It is hard to imagine a world without lubricants. With no cars, boats, airplanes (or even bicycles) to transport us, without tractors to plant and process crops, without machines to process metal and plastics into everyday containers, without HVAC systems to keep us comfortable, without refrigerators to keep our food fresh, and without the lubricants needed for almost all of our creature comforts, our lives would grind to a halt. Indeed, we would quickly revert to pre-Industrial Revolution status. Such is the importance of the humble lubricant.
Lubricants help to separate moving parts, reduce friction, transfer heat, remove contaminants, transmit power, protect against wear and corrosion, and provide a seal to keep gases in or out. Because lubricants are so ubiquitous and serve so many different functions, they come in many varieties and have properties well-suited to meet the demands of a particular application. Most lubricants include a “base oil” and other components. Most base oils are paraffinic, naphthenic, or aromatic mixtures that derive from petroleum and thus depend on the availability of non-renewable resources.
Various synthetic oils are known, including poly(alpha-olefin)s, synthetic esters, polyalkylene glycols, phosphate esters, and other materials. Many of these materials are designed for special needs that cannot be satisfied by hydrocarbon lubricants.
Polyol esters and other esters of mono-, di-, or polycarboxylic acids have been used for some lubricant applications. The ester functionality provides thermal stability helpful for some uses. Usually, the polyol esters are built from typical low-molecular-weight building blocks that are staples of the chemical industry and most frequently come from petrochemicals. In some cases, vegetable oils have been used as a source of raw materials.
Waste thermoplastic polyesters, including waste polyethylene terephthalate (PET) streams (e.g., from plastic beverage containers), provide an abundant source of raw material for making new polymers. Usually, when PET is recycled, it is used to make new PET beverage bottles, PET fiber, or it is chemically transformed to produce polybutylene terephthalate (PBT). Ideally, these recycled materials could find other applications outside the field of thermoplastic polyesters. Lubricants provide a largely unexplored yet diverse field into which these recycled materials can be re-purposed and up-cycled.